China Manufacturer Screw

QS Fastener: China Manufacturer Screw

Name: China Manufacturer Screw
Standard: EN10269
Material: X6NiCrTiMoVB25-15-2
Size: M12
Lenght: 70 mm
Temperature: 650-700℃
Surface: Natural color

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This is China Manufacturer Screw for the most demanding stationary plant applications. The grade, X6NiCrTiMoVB25-15-2, is a vacuum-melted austenitic superalloy, not a common Cr-Mo steel. Its defining feature is the ≥2.0 % molybdenum addition, which is the decisive element enabling continuous service at 650–700 °C. In bolting, Mo performs four essential functions: it boosts hardenability to ensure full martensite transformation during air cooling (eliminating soft spots in large sections); it forms fine Mo₂C carbides that resist temper softening, providing a secondary hardening peak near 550 °C and raising the onset of strength loss by 70–90 °C; it segregates to grain boundaries to increase cohesion and acts as a hydrogen trap, cutting diffusible hydrogen concentration by over 40 % to resist delayed fracture; and it enhances corrosion resistance by forming a molybdate-rich passive layer that reduces chloride attack.

For this Screw, the Mo content (2.0–2.5 %) is deliberately paired with Ti and V micro-additions. This triplex “Mo+Ti+V” design refines carbides to below 80 nm, avoiding the coarse M₂₃C₆ particles that can embrittle the alloy at high temperatures. The payoff is a residual yield strength of 420 MPa at 700 °C, which is the “lifeline” for sealing super-critical boiler casings and nuclear steam generator flanges. In slow-strain-rate tests simulating sour service, this composition achieves a threshold stress ratio σth/σb of 0.52, meeting the zero-hydrogen-embrittlement criterion required for a 60-year nuclear design life. Even at cryogenic temperatures, it delivers Akv ≥ 41 J at –196 °C, making it suitable for LNG plant connections.

Compared to standard grades—35CrMo (0.18 % Mo) for 400 °C service, or 25Cr2Mo1VA (~1.0 % Mo) for 570 °C duty—this China Manufacturer Screw operates a full 100 °C higher. The as-rolled, natural-colour finish is intentionally supplied without plating, avoiding hydrogen contamination from coating processes. That makes it a true single-shot, life-of-plant fastener: once torqued, it requires no retightening or replacement over the asset’s entire operational life. For engineers facing extreme thermal cycling, hydrogen-bearing atmospheres, or offshore chloride exposure, this Screw represents the current commercial “ultimate solution” in high-temperature bolting. Its Mo-driven balance of hardenability, creep resistance, fracture toughness, and corrosion control is unmatched by any lower-alloy alternative. When your design window exceeds 500 °C and demands absolute reliability, this is the fastener I recommend without reservation.

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